Volatile Fatty Acid Recovery from Anaerobic Fermentate: Focusing on Adsorption and Desorption Performances

The purification and concentration of volatile fatty acids (VFAs) after acidogenic fermentation represent the key steps for their industrial use. In this study, different batch adsorption tests were performed on single VFAs using powdered activated carbon (PAC), Lewatit VP OC 1065, Amberlyst A21, and VFA mixtures using Lewatit and Amberlyst. Adsorption yields of approximately 70% for PAC and 86-96% for Lewatit and Amberlyst were achieved on the single VFA tests at an initial concentration of S g/L. The VFA mixture tests at 25 g/L showed lower yields: 40 and 27% for Lewatit and Amberlyst, respectively. Batch desorption tests were performed adopting two desorbents, ethanol, and water at various NaOH concentrations (1, 0.1, and 0.01 M) and at decreasing volumes (5, 3, and 2 mL). The optimization of the adsorption and desorption operations allowed the final VFA concentrations of 85-90 g/L to be reached. The best adsorbent, Lewatit, and the best desorption conditions were applied on a real fermentate with an initial VFA concentration of approximately 18 g/L, obtaining a final VFA content three times higher than in the original solution.